FIG. 9 illustrates a double-row tapered-roller bearing unit that is used in comparatively heavy automobiles such as small trucks or large passenger vehicles for rotatably supporting the wheels with respect to the suspension. This double-row tapered-roller bearing unit includes an outer ring 1 that is an outer-diameter-side bearing ring member, a hub 2 that is an inner-diameter-side bearing ring member, and plural tapered rollers 3.
The outer ring 1 includes double-row outer-ring raceways 4, 5 that are formed on the inner circumferential surface thereof, and a stationary-side flange 6 that is formed on the outer-circumferential surface thereof for joining and fastening the outer ring 1 to the knuckle of a suspension. Of the double-row outer-ring raceways 4, 5, the first outer-ring raceway 4 that is located on the inside in the axial direction, which is one side in the axial direction, and the second outer-ring raceway 5 that is located on the outside in the axial direction, which the other side in the axial direction, have partial conical surfaces that are inclined in directions so that the diameters become larger going in directions going away from each other in the axial direction. The “inside” in the axial direction is the center side in the width direction of the vehicle when assembled in an automobile, and is the right side in FIG. 1 and FIG. 9, and is the top side in FIG. 3 and FIG. 8. On the other hand, the “outside” in the axial direction is the outside in the width direction of the vehicle, and is the left side in FIG. 1 and FIG. 9, and is the bottom side in FIG. 3 and FIG. 8.
The hub 2 is concentrically arranged with the outer ring 1. The hub 2 includes double-row inner-ring raceways 7, 8 that are located on the inside-end section and the middle section in the axial direction of the outer-circumferential surface thereof, and a rotating-side flange 9 that is formed in the portion near the outside end in the axial direction that protrudes in the axial direction from the inner-diameter side of the outer ring 1 for supporting and fastening a wheel. Of the double-row inner-ring raceways 7, 8, the first inner-ring raceway 7 that is located on the inside in the axial direction and the second inner-ring raceway 8 that is located on the outside in the axial direction have partial conical surface that are inclined in directions so that the diameters become larger going in directions away from each other in the axial direction.
The hub 2 includes a circular ring-shaped first inner ring 10 with the first inner-ring raceway 7 formed on the outer-circumferential surface thereof, a circular ring-shaped second inner ring 11 with the second inner-ring raceway 8 formed on the outer-circumferential surface thereof, and a hub main body 12 that is a shaft member and that is integrally formed with the rotating-side flange 9. The first inner-ring raceway 7 and the second inner-ring raceway 8 are respectively provided between a small rim section that is provided on the small-diameter-side end section and a large rim section that is provided on the large-diameter-side end section of the outer-circumferential surface of each of the first inner ring 10 and the second inner ring 11. The second inner ring 11 is press-fitted with an interference fit onto the outside half section in the axial direction of a cylindrical-shaped fitting surface section 13 that is provided so as to extend from the inside end section to the middle section in the axial direction of the outer-circumferential surface of the hub main body 12. The first inner ring 10 is press-fitted with an interference fit onto the inside half section in the axial direction of the fitting surface section 13. The large-diameter-side end surface of the first inner ring 10 is held by a crimped section 15 that is formed by plastically deforming the cylindrical section 14 that is provided on the inside end section in the axial direction of the hub main body 12 outward in the radial direction. Therefore, the first inner ring 10 and the second inner ring 11 are held on both sides in the axial direction by a step side surface 16 that exists on the outside end section in the axial direction of the fitting surface section 13 and the crimped section 15, and in this state, are joined and fastened to the hub main body 12.
Plural tapered rollers 3 are located between the first outer-ring raceway 4 and first inner-ring raceway 7, and between the second outer-ring raceway 5 and the second inner-ring raceway 8, and are rotatably held by the cage 17. Combined seal rings 18 are assembled between the inner-circumferential surface of the inside end section in the axial direction of the outer ring 1 and the outer-circumferential surface of the large-diameter-side end section of the first inner ring 10, and between the inner-circumferential surface of the outside end section in the axial direction of the outer ring 1 and the outer-circumferential surface of the large-diameter-side end section of the second inner ring 11; and these seal rings 18 cover the openings on both ends in the axial direction of the cylindrical-shaped space where the tapered rollers 3 are located. A spline hole 19 is provided in the center section in the radial direction of the hub main body 12 for receiving the tip-end section of the drive shaft and forming a spline engagement with the drive shaft.
When assembling the hub 2, as the crimped section 15 is formed, the inner ring 10 is elastically deformed so that the large-diameter-side end section of the first inner ring 10 is elastically expanded radially more than the small-diameter-side end section, which changes the inclination angle of the first inner-ring raceway 7. Therefore, as disclosed in JP 4,019,548 (B2), taking the change in the inclination angle of the first inner-ring raceway 7 into consideration, it is necessary to adjust the inclination angle of the first inner-ring raceway 7 in the state before forming the crimped section 15. When this kind of adjustment is not performed, there is a possibility that the contact state between the rolling contact surfaces of the tapered rollers 3 and each of the raceways 4, 5, 7, 8 will become improper, and that maintaining the durability of the double-row tapered-roller bearing unit will become difficult. The inclination angle of the first inner-ring raceway 7 is the inclination angle of the first inner-ring raceway 7 with respect to the center axis of the first inner ring 10, and the inclination angle of the second inner-ring raceway 8 is the inclination angle of the second inner-ring raceway 8 with respect to the center axis of the second inner ring 11.
However, taking the change in the inclination angle of the first inner-ring raceway 7 into consideration, and adjusting only the inclination angle of the first inner-ring raceway 7 in the state before forming the crimped section 15, is not sufficient for placing the inclination angles of both the first inner-ring raceway 7 and the second inner-ring raceway 8 within the proper range, and particularly, is not sufficient for making these inclination angles the same after the hub 2 has been assembled. Therefore, from the aspect of improving the durability of a double-row tapered-roller bearing unit, there is still room for improvement.